Yes, diamond is classified as a metamorphic rock. It is formed under extreme pressure and temperature conditions deep within the Earth’s mantle. Specifically, diamonds originate from carbon-containing minerals that undergo a transformation as they are subjected to high pressure and temperatures that can exceed 1,000 degrees Celsius (1,832 degrees Fahrenheit). This transformation allows the carbon atoms to bond in a crystal structure that results in diamond formation.
Metamorphic rocks, by definition, are formed from the alteration of existing rocks—either igneous, sedimentary, or other metamorphic rocks—due to geological processes. In the case of diamonds, they can also be associated with the metamorphism of carbon-rich sediments. Therefore, while diamonds are often considered as gemstones, they are indeed a type of metamorphic rock due to their geological origins and formation process.